Without getting too long-winded............. . Rome changed from republic to emperor to appease Julius Caesar, who rather held the trump card when he crossed the Rubicon (ie. he had a stonking great army with him).. . What made Rome successful is a more difficult question to answer, but I'd put it down to these three main factors,. . 1. Excellent professional military machine. 2. Assimilation of other cultures into the Roman way of life. 3. The expectation of a higher standard of living under Roman rule. . **********************************************************************. . OK Crazy Tigger, I'll accept the fact that Julius Caesar did not carry the title of Emperor and I guess you'd therefore say that this distinction should lie with Octavian (Augustus). I think, however, that Julius Caesar is widely regarded as the first Roman Emperor as per the link below.